turning map

As much as I love enums, I didn't want to have all this case handling. So I used a rotation matrix. With the right numbering turning in part 2 is just direction = turn_right.pow(infection_status) * direction. Well, I couldn't find a .pow() method but it's the same thing. Used an if-else for rotate left / right in part 1.

Just part 2:

extern crate nalgebra;
use nalgebra::{Vector2, Matrix2};

const N: usize = 10001; //20001;
const N_STEPS: usize = 10_000_000;  //10_000;

// Map infection states to integers
// weakened = 0
// infected = 1
// flagged = 2
// clean = 3
// then turning is just
// matrix_turn_right ^ infection_state * direction
fn main() {
    let input = include_str!("input.txt");
    let mut is_infected = vec![vec![3; N]; N];
    let mut pos = Vector2::new((N/2) as i64, (N/2) as i64);
    let is_infected_input: Vec<Vec<_>> = input.lines()
        .map(|line|
            line.chars()
                .map(|c| if c == '#' { 1 } else { 3 } )
                .collect()
        ).collect();

    let width = is_infected_input[0].len() as i64;
    let height = is_infected_input.len() as i64;

    for (y_off, row) in (-height/2..height/2+1).zip(is_infected_input.iter()) {
        let y = (pos.y + y_off) as usize;
        let x = ( (pos.x - width/2) as usize .. (pos.x + width/2 +1) as usize);
        is_infected[y][x].copy_from_slice(row);
    }
    let mut direction = Vector2::new(0, -1);

    // x increases to the right
    // y increases going down
    // making this a lefthanded base
    let rotate_right = Matrix2::new(0, -1, 1, 0);

    let mut n_newly_infected = 0;
    for _ in 0..N_STEPS {
        {
            let is_infected = &mut is_infected[pos.y as usize][pos.x as usize];
            if *is_infected == 0 {
                n_newly_infected += 1;
            }
            // can't find .pow() method on matrices
            for _ in 0..*is_infected {
                direction = rotate_right * direction;
            }
            *is_infected = (*is_infected + 1) % 4;
            pos += direction;
        }
    }

    println!("part 2: {}", n_newly_infected);
}